A large and growing market for laser processing is PCB manufacturing. Traditionally, this market used carbon dioxide and excimer lasers, but increasingly turned to UV DPSS lasers. The migration to UV DPSS laser technology is driven by multiple factors. For example, laser processing is required to achieve a smaller special processing area with higher precision and density, and UV wavelengths can process multiple types of materials with high quality. In addition, the production cost and purchase cost of UV DPSS lasers are falling.
The Spectra-Physics Talon? UV product series (shown in Figure 1) consists of industrial UV lasers with nanosecond pulse widths. The Talon product series are highly versatile, with a variety of power, energy and pulse repetition frequency (PRF) configurations. For example, 15 W UV Talon provides high pulse energy of 300 μJ at 50 kHz PRF, which can process a larger area in thicker materials (such as FR4 rigid PCB). On the other hand, 20 W UV Talon has a lower maximum pulse energy, but maintains a higher output power level at a very high PRF. These parameters are very suitable for processing thinner materials with tightly focused beams, and can achieve high-speed, high-resolution processing.
Advantages of UV DPSS lasers in PCB manufacturing
With the shrinkage of electronic components and the improvement of performance, the demand for small and thin flexible PCBs for mounting electronic components is growing rapidly. Flexible PCBs are usually made using material layers with a thickness of a few micrometers to several tens of micrometers. The materials used include copper (Cu) foil, polyimide (PI) boards, and adhesives that can form various laminated structures. A typical flexible PCB material consists of a 12 μm thick PI layer laminated between two Cu foils of similar thickness. In flexible PCB manufacturing, laser processes may include blind and through hole drilling, straight and contour cutting, and 2D pattern formation. Considering the high power and high PRF of Talon UV lasers, MKS has been able to optimize various high-speed processes for flexible PCB materials.
Advantages of UV DPSS lasers in PCB manufacturing
Figure 2 A cross-sectional view of drilling through holes in a flexible PCB using a Spectra-Physics Talon UV nanosecond laser. The flexible PCB layer is a Cu/PI/Cu laminate. The through hole is cut with an 80 μm diameter trephine. The average burr height obtained is less than 2 μm.
By optimizing the scanning speed and PRF to achieve proper spot overlap in the material, it is possible to achieve high-quality cutting and drilling performance at high speeds. The high average power of Talon laser at high PRF can provide enough pulse energy to ablate Cu materials at up to several hundred kHz. Using Talon 355-20 laser can cut Cu/PI/Cu laminates at a speed exceeding 450 mm/s while working at 500 kHz.
As shown in Figure 2, the cutting quality is very good, the burrs are the smallest, and the HAZ is also small. The Talon UV laser has also been tested for high-speed impact drilling of blind holes in similar Cu/PI/Cu laminates. In this case, the thickness of the middle PI layer is doubled to 25 μm, high-quality through holes with diameter openings less than 30 μm are processed, and the high repetition frequency is used to minimize the drilling time. Using a Talon laser operating at 300 kHz, only 20 pulses are required to drill each hole, which is equivalent to 15,000 holes per second.
Thin PI film is also widely used in flexible PCB manufacturing as a protective film material to protect circuits from harsh environments, similar to solder masks in thick PCB manufacturing. Due to the strong optical absorption of the material and subsequent light ablation, the UV wavelength is very effective for high-quality, high-precision processing of PI. The commonly used thickness of the material is 12-25 μm, and the high PRF, low energy laser source is used to achieve the best cutting of these materials. The Talon serial laser is the ideal choice to meet these requirements and can achieve a wide range of cutting speeds.